The present invention relates to an electronic image pickup apparatus, such as an electronic camera, comprising a light beam adjusting unit including an aperture and/or a shutter.
Exposure of an electronic image pickup apparatus, for example, a digital camera, is controlled by programmed exposure using the combination of an exposure and an aperture.
First, as regards the aperture type, a type in which common blades serve as both an aperture and a shutter is conventionally known as an aperture used in a silver salt film camera, or the like. In the case of an image pickup element, since it has a narrow latitude, exposure accuracy must be higher than in the case of silver salt film is required. However, an aperture of the conventional type having a plurality of aperture blades cannot precisely reproduce an aperture diameter. Under the circumstances, a so-called turret-type aperture, in which a suitable aperture plate having a fixed open diameter is inserted in the optical path, is employed.
Secondly, as regards the shutter type, an electronic shutter of an image pickup element is generally used, which is simple and does not require a mechanical system. However, with only an electronic shutter, the image pickup element is kept irradiated with light reflected by an object, even after the charge storage period expires. Therefore, noise charge is liable to be generated in a charge storage section, a charge transfer path or a surrounding portion before and after a photographing time. If the noise charge enters the charge transfer path, the quality of an image will be deteriorated. This is called smear noise.
The smear noise can be prevented, if a mechanical shutter for shielding the image pickup element from light reflected by an object is provided in the photographing optical system, so that the mechanical shutter is driven at substantially the same time as the completion of exposure to shield the image pickup element from external light.
Particularly, in an image pickup element having a number of pixels, the signal charge transfer time is long, resulting in higher probability of influence by smear, a mechanical shutter is required in addition to an electronic shutter. Thus, it is necessary to add the function of a mechanical shutter to an aperture of the turret type which can provide an accurate aperture. From this viewpoint, it is proposed to improve an aperture of, for example, the turret type, so as to also serve as a shutter by arranging a shielding section in proximity to the aperture opening of the turret aperture plate. This aperture shutter system is disclosed in Published Japanese Patent No. 2622296, etc. Further, Jpn. Pat. Appln. KOKAI Publication No. 7-111616 discloses a system in which an aperture and a shutter are driven by a single motor.
However, in the case where the turret type aperture also functions as a shutter, it is necessary to provide a relatively large shielding section in the aperture opening. For this reason, the diameter of the aperture plate as a whole is large, and resulting in the drawback of the large apparatus size. In both the aforementioned prior art references, although a single driver is used, it is required that the opening of the aperture section be positioned accurately and that the shutter section open and close the blades at a high speed. It is not necessarily easy to satisfy both requirements by means of the single driver as disclosed in the prior art references.
Further, in a portable apparatus using a battery, the supplied voltage may be lower than the voltage which allows photographing by a drop in source voltage, depending on the drive timing of the shutter and the aperture. In this case, a normal operation cannot be performed.
An object of the present invention is to provide a electronic image pickup apparatus having an aperture shutter unit, which can be assembled easily and compact, and in which a battery lifetime is long and a stable operation is expected.
To achieve the above object, the electronic image pickup apparatus of the present invention has the following constitution. The features of the present invention other than the following will be clarified in the description of the embodiments.
The electronic image pickup apparatus of the present invention comprises: a holding barrel; a lens frame supported by guide shafts inside the holding barrel and slidable and movable in a direction of an optical axis; a light beam adjusting unit including an aperture and/or shutter for mechanically adjusting a light beam passing through the lens frame; and an image pickup element for converting an object image passed through the light beam adjusting unit to an electrical signal,
the light beam adjusting unit comprising: a base plate arranged perpendicular to the optical axis inside the lens barrel; an aperture member and/or a shutter member attached to the base plate; and an aperture driver for driving the aperture member and/or a shutter driver for driving the shutter driver, arranged on the base plate.